Concrete is high in resistance to various environments, and moreover, strongly alkaline, and hence is used for concrete structures. Due to the strong alkalinity of concrete, a passive film is formed on the surface of reinforcing bars placed inside a concrete structure, and hence the reinforcing bars are protected from the corrosion due to, for example, water or chlorine from the outside. Consequently, concrete structures are known as structures high in durability.
However, concrete structures having been considered to have high durability are degraded in durability due to, for example, neutralization, salt damage, frost damage or alkali-aggregate reaction, and doubt comes to be cast on the service life of concrete structures as structures.
Accordingly, methods for repairing such a degraded concrete structure have been proposed. For example, Japanese Patent Laid-Open No. 62-265189 (Patent Literature 1) proposes a method in which aqueous solutions of nitrites are used as anticorrosives for reinforcing bars, penetrating deep into inside concrete.
Japanese Patent Laid-Open No. 2007-126309 (Patent Literature 2) states that in order to produce a gelled substance contributing to repairing a concrete structure, calcium ions in the concrete and an alkali silicate penetrant are necessary, and in order to promote the production of the gelled substance, it is necessary to set the pH of the concrete at 11 or less. On the basis of such an observation, Patent Literature 2 proposes a method in which a calcium salt aqueous solution (for example, a calcium chloride aqueous solution) and an alkali silicate penetrant (for example, sodiumsilicate) are separately allowed to penetrate into concrete, and thus a gelled substance is produced.